The Impacts of Cluster-Thinning and Cluster-Zone Leaf Removal on the Hormone Content of Pinot Noir Grape Berries
During the third year, we confirmed that the relative developmental stage of a berry was not fully a function of the flowering time, but was more associated with seed development. Therefore, our study reinforced the use of a new seed index (SI), also named SB or seed weight-to berry weight ratio to describe berry developmental stage. We have identified and optimized a selection method for selecting individual fruits of cluster at discrete stages using multivariate statistical tools in order to minimize inherent biological variability existing within a grape cluster. The analysis of bioactive forms of auxin, abscisic acid, cytokinin, brassinosteroid, gibberellin, jasmonic acid, and salicylic acid revealed a clear spatial and temporal distribution for most of them during the major critical steps of berry development.
Indeed, we were able to correlate the accumulation dynamics of most of them with major physiological events occurring during berry development. We were also successful in quantifying the effects of two common viticulture practices, cluster-thinning and cluster-zone leaf removal, on two major plant hormones responsible for the ripening initiation (ABA and Auxin). The analysis of the conjugate forms, precursors of, and catabolites of those bioactive analytes revealed specific regulatory pathways. These observations will lead to develop new working hypothesis to explain their mode of regulation in a tissue and developmental context. Based on our results, we will investigate in a near future other layers of biological information including gene expression. Encouraging results during the second year showing a peak ethylene during the ripening will need further investigation in order to prove the real contribution of endogenous ethylene production during grape berry development. From this study, we expect to have at least two peer-reviewed papers published as a result of this funded research and we will propose the results for oral presentation at the next conference of the American Society of Enology and Viticulture.